Use of lime in heavy-media separation process



Patented Sept. 18, 1945 USE OF LIME IN HEAVY-MEDIA SEPARATION PROCESS Norman Hedley and John Joseph Kress, Stamford, Conn, asslgnors to American Cyanamid mpany, New- York, N. Y., a corporation of No Drawing. Application November 17, 1942,

Serial No. 465,910

.6 Claims. (Cl. 209173) This invention relates to an improved process of beneficiation of ores containing carbonates by the sink and float process in a heavy medium.

Heavy media processes for beneficiation of ores by sink and float processes have attained great the ore, frequently gangue, float. It is necessary to remove adherent medium from both the float product and the sink product and a cleaning process is, therefore, necessary because usually the medium solids are sufliciently valuable so that they cannot be thrown away economically. This has made an improved heavy media process using magnetizable solids, particularly useful in the treatment of many ores, as the medium adhering to the sink and float product can be washed off and cleaned from associated impurities by simple magnetic cleaning. Among the magnetizable solids which can be used in this improved heavy media process ferrosilicon has many advantages as it has a high specific gravity and at the same time shows quite adequate rust resistance for most operations.

An important class of ores which can be bene-,

ficiated by the use of heavy media are the carbonate ores, of which those containing alkaline earth metal carbonates such as magnesite are of medium becomes entirely unusable. As it is obviously economically impractical to discard ferro-' silicon medium daily it appeared that magnesite ores could not be beneiiciated satisfactorily by sink and float process .using-ferrosilicon.

According to the present invention it has been found that carbonate'ores and particularly ores containing carbonates of the alkaline earth metals, especially magnesite, can be treated satisfactorily by a sink and fioat process with ferrosilicon medium if there is present in the medium a suflicient amount of anion of an alkaline earth metal in a form in which it is capable of reacting with carbon dioxide or bicarbonates. We have determined that carbon dioxide is a serious factor in deterioration of ferrosilicon medium in the presence of carbonates such as carbonates of the alkaline earth metals. While it seems probable that the action of carbon dioxide or of bicarbonates formed therewith on the ferrosilicon is a major factor in the deterioration of the ferrosilicon medium and may perhaps be the only factor, it is not desired to limit the invention to a theory in which the action of carbon dioxide is the only factor.

Within considerable limits the process of the,

present invention appears to be relatively unaffected by pH although of course an extremely acid circuit will cause rapid decomposition of the ferrosilicon. The relative unimportance of pH within considerable limits is shown by the fact that alkaline earth metal compounds, such as calcium sulfate, which are capable of reacting with carbon dioxide are effective and it is not necessary to use a basic alkaline earth metal compound, such as calcium hydroxide. However, calcium hydroxide is the cheapest alkaline earth metal compound available and as it is also one of the best for use in the present invention it is preferred. Barium hydroxide and strontium hydroxide are of about equal activity but more expensive. The particular compound which sets free in water solution the alkaline earth metal ion is, therefore, not of great importance, although there is-some slight difference in efiectiveness between different compounds.

The present invention should not be confused with the use of alkalies to prevent the attack of water on ferrosilicon at low pHs in the absence of carbonate ores. This phenomenon, that is to say, the reaction of ferrosilicon with water in acid mediums is well known and can be counteracted to a large extent by the addition of any alkali. Of course, hydroxides of the alkaline earth metals will also produce this result, but it is apparently an entirely different result than that of the present invention because the improvements of the present invention are obtained when the alkaline earth metal compounds are not alkalies and the addition of alkalies which do not contain alkaline earth metal ions will not effect protection in the case of ferrosilicon media used with carbonate ores.

The invention will be described in greater detail in conjunction with the followin examples:

Example 1 mixed with suflicient water to produce a medium having a specific gravity of 2.89. Th medium was transferred into a small cone and held in suspension by blowing air therethrough. 2.2 parts of a magnesite ore from the Pacific Northwest was added, the ore being sized i" tomesh, corresponding to the size of ore suitable for commercial treatment. Further samples of the same medium were prepared andrall oi the sample media were agitated by aeration in the cone for a period of 48 hours, samples being taken at 24 hour intervals. The first test sample received no addition; the second 7 lbs. per ton of calcium hydroxide; the third 18 lbs. per ton of barium hydroxide containing 8 molecules of water; the fourth 12 lbs. per ton of strontium by droxide containing 8 molecules of water; the fifth 8 lbs. per ton of calcium sulfate containing 2 molecules of water; and the sixth was aerated with air from which all carbon dioxide had been removed by passing through a 33% KOH solution. The results of the tests are shown in the following table, the viscosity being measured in iecting fragments of the ore of a size suitable for sink and float separation to the action of a medium comprising an aqueous suspension of finely divided ierrosilicon and having a specific gravity greater than the lighter constituents of the ore, whereby the lighter constituents float and the heavier constituents slnk, removing the floating constituents and sinking constituents, removing adherent medium solids therefrom, said process involving extensive exposure to the atmosphere, reusing said medium solids, and maintaining the viscosity of the medium-by the addition of a sufflcient amount of a compound oi an alkaline earth metal included in the group consisting of calcium, strontium and barium, and capable of reacting with gaseous carbon dioxideto maintain at all times alkaline earth metal ions in the medium.

2. A method of beneficiating ores containing carbonates of the alkaline earth metals as a major constituent of the ore by the sink and float process, which comprises subjecting fragments of the ore of a size suitable for sink and float separation to the action of a medium comprising an aqueous suspension or finelv divided ferroseconds by the Marsh funnel test (500/500). silicon and having a specific gravity greater than Characteristics of Fc-Bi medium Test No; Reagent added, lbalton Fe-Si Start of tent Alter 24 hours Alter 48 hours Viscosity Appearance Viscmlty Appearance Viscosity Appearance Seconds Seconds Seconds None- 22.5 Clean, black" 25.5 Green 41.0 Thick light green. 'llbs-lton GB(OH)Q 23.0 o 22.5 Clean, black- 22.0 Clean, black. 18lbs./tonBa(0H):.8Hi0. 22.0 n 21.5 .do 22.0 Do. 12 lbs.lton Sr(0H)s.8Ha0 23. 5 o 23. 0 Do. -lton c880i.2H2o 23.5 c.o 25.0 Do. 00: removed 23, 0 r n 22. 0 Do.

Example 2 A ferrosilicon medium was prepared as described in Example 1 and used for the sink and -float separation of dolomite from magnesite.

The process'was continued for many days and 3 parts of calcium hydroxide were added to the medium per day. Deterioration of the medium was practically negligible there being substantially no increase in viscosity and the medium remaining-a clean black without gelatinous green slime. The addition of lime did not afiect in any way the sink-and float procedure, except that slightly less ferrosilicon was needed to produce the same specific gravity as the added lime contributed slightly to increase the specific gravity.

A control test was run with the same ore but without the addition of calcium hydroxide. The viscosity of the medium increased rapidly and after less than 48Vhours it had become so viscous as to be practically unusable. The same characteristic gelatinous green slime was also noted. 4

The improved process of the present invention is applicable to other ores containing magnesium or other alkaline earth carbonates or carbonates of other metals, the action with magnesium carbonate being typical. The rate of deterioration of the medium will vary somewhat with different carbonate ores depending to a considerable extent at least on the tendency of the carbonate to form a bicarbonate by reaction with carbon dioxide of the air.

We claim:

l. A method of beneficiating ores containing carbonates as a. major constituent of the ore by the sink and 'float process, which comprises sub- I the lighter? constituents oi the ore, whereby the lighter constituents float and the heavier constituents sink, removing the floating constituents and sinking constituents, removing adherent medium solids therefrom, said process involving extensive exposure to atmosphere, reusing said medium solids, and maintaining the viscosity of the medium by the addition of a sufllcient amount of a compound of an alkaline earth metal included in the group consisting of calcium, strontium and barium, and capable of reacting with gaseous carbon dioxide to maintain at all times free alkaline earth metal ions in the medium.

3. A method of beneficiating ores containing magnesium carbonates as a major constituent of the ore by the sink and float process, which comprises subjecting fragments of the ore of a size suitable for sink and float separation to the action of a medium comprising an aqueous suspension of finely divided ferrosilicon and having a specific gravity greater than the lighter constituents of the ore, whereby the lighter constituents float and the heavier constituents sink, removing the floating constituents and sinking constituents. removing adherent medium solids therefrom, said process involving extensive exposure to the at- 'nosphere, reusing said medium solids, and maintaining the viscosity of the medium by the addition of a sufflcient amount of a compound of an alkaline earth metal included in the group consisting of calcium, strontium and barium, and capable of reacting with gaseous carbon dioxide to maintain at all times free alkaline earth metal ions in the medium.

4. A method of beneficiating ores containing carbonates as a major constituent of the ore by the sink and float process, which comprises subiecting fragments of the ore of a size suitable for sink and float separation to the action of a medium comprising an aqueous suspension of finely divided ferrosilicon and having a specific gravity greater than the lighter constituents of the ore, whereby the lighter constituents float and the heavier constituents sink, removing the floating constituents and sinking constituents; removing adherent medium solids therefrom, said process involving extensive exposure to the at-- mosphere, reusing said medium solids, and maintaining the viscosity of the medium by the addition of calcium hydroxide to maintain at all times free calcium hydroxide in'the medium.

1 5. A method of beneflciating ores containing carbonates of the alkaline earth metals as a major constituent of the ore by the sink and float process, which comprises subjecting fragments of the ore of a size suitable for sink and float separation to the action of a medium comprising an aqueous suspension of finely divided a specific gravity greater than the lighter constituents of the ore, whereby the lighter constituents float and the heavier constituents sink,

ierrosilicon and having a specific gravity greater than the lighter constituents of the ore, whereby the lighter constituents float and the heavier constituents sink, removing the floating-constituents and sinking constituents, removing adherent meremoving the floating constituents and sinking constituents, removing adherent medium solids therefrom, said process involving extensive exposure to the atmosphere, reusing said medium solids and maintaining low viscosity by the addition of sumcient calcium hydroxide to maintain at all times free calcium hydroxide in the medium.

NORMAN HEDIEY. JOHN JOSEPH KRESS. 

